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Timing Ok?
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Author:  Brik Nuts [ Fri Jan 29, 2010 4:49 pm ]
Post subject:  Timing Ok?
Hey I hav put on a timing chain........does it look like its correct?
Its a duplex chain and the sprockets hav different markings on them I would assume that the markings are stamped as a universal marking?

Image
Author:  mini_mad_matt [ Fri Jan 29, 2010 6:25 pm ]
Post subject: 
I'm no expert but that looks right to me. If you're worried about the camshaft being marked incorrectly you could check its position by which valves are rocking (stick the pushrods so you can see them move) I forget if its 1 or 4 that should be rocking or thereabouts in your pic.

As for the crankshaft thats in the right spot


If you put have the chain so tension is on the bottom side of the chain do the marks line up a bit better?
Author:  1018cc [ Fri Jan 29, 2010 6:27 pm ]
Post subject: 
The keyways are in the correct position for 'lining up the dots'. This is fine for a standard cam as the margin for error is high.

The dots on the gears line up when #4 is at TDC (firing stroke) NOT #1.

<edit> make sure you have shimmed the crank gear correctly and have the correct oil slinger!
Author:  Rodney [ Fri Jan 29, 2010 6:48 pm ]
Post subject: 
Quote:
make sure you have shimmed the crank gear correctly and have the correct oil slinger!



What shims??? Don't you just use the same oil slinger???

Cheers
Author:  1018cc [ Fri Jan 29, 2010 6:53 pm ]
Post subject: 
There is sometimes a different oil slinger used depending on whether you have a simplex or duplex timing chain. I remember people telling me that when I changed mine over to a duplex chain a while back.

As for the shims, there are shims that space out the crank gear to ensure that the chain runs smoothly (and it not trying to bend across to the cam gear). I think I took one or two shims off of my crank in order to get my gears to line up properly.

Also, what you put the timing cover back on, just do the bolts up loosely and put the balancer on. This will line the timing cover up in the correct spot and you will *hopefully* avoid an oil leak. After the balancer has been put on you can tighten up the rest of the bolts around the timing cover.
Author:  GT mowog [ Fri Jan 29, 2010 7:26 pm ]
Post subject: 
Rodney wrote:
Quote:
make sure you have shimmed the crank gear correctly and have the correct oil slinger!



What shims??? Don't you just use the same oil slinger???

Cheers


I've been building up these engines for longer than I care to remember and yes, I have come across 2 types, OK and stuffed, but the latter are the more rarer of the 2. No, seriously, they are both the same for simplex or duplex - P/N 12A1148.
Author:  mini7boy [ Fri Jan 29, 2010 7:28 pm ]
Post subject: 
you don't mention anything about the cam or the engine's build spec, but any engine that is worth your time and money to build is also an engine that is worth having its cam timing checked and set correctly. For the dot-to-dot method to work, you have to assume that the cam was ground correctly and that both the crank and cam sprockets were machined correctly. That's three parts, any one of which could be imprecise, that could affect your cam timing adversely. Since an error as small as 2-3 degrees can make a very significant difference in performance, why would anyone assemble an engine without taking the time to setup the cam timing correctly?

It's just like taking the time to torque the fasteners, adjust the valves or set the ignition timing, in my opinion.

If you can, or won't, do it right, why bother at all?
Author:  drmini in aust [ Fri Jan 29, 2010 7:39 pm ]
Post subject: 
What he said ^^^
Further errors come in if the engine has been line bored- this seriously retards the timing (apart from making the chain loose).
Also, some sprockets fitted to motors out here in the 70s, deliberately retarded the timing for improved emissions.

Bottom line-
You won't know what the actual valve timing is, if you don't bother to check it. :wink:
Author:  Brik Nuts [ Sat Jan 30, 2010 5:12 pm ]
Post subject: 
Hey thanks for the replys.
Its a 1275gt engine it has a standard 1275 cam but I need to check the bores on it.

Best Idea is to put the head on tighten it down? then check the timing before its all bolted up?
Author:  drmini in aust [ Sat Jan 30, 2010 6:46 pm ]
Post subject: 
Yes that is the best way, particularly with a chain drive.
Author:  TheMiniMan [ Sat Jan 30, 2010 10:34 pm ]
Post subject: 
looks like it`s about 2 maybe 3 deg out to me :-)
Author:  david rosenthal [ Sun Jan 31, 2010 12:43 am ]
Post subject: 
TheMiniMan wrote:
looks like it`s about 2 maybe 3 deg out to me :-)


the mark on the crank tooth is not in-line with the tooth and I reckon for what it's worth that Matt is right.
I use some old push rods cut off and clamped with some old valve springs to put some resistance on the cam [like normal valves/rockers] and rotate the engine to check the cam timing before the head goes on.
Author:  drmini in aust [ Sun Jan 31, 2010 5:52 am ]
Post subject: 
It's important to check alignment of the 2 marks and sprocket centres with a straightedge, BEFORE putting it on the motor. I have pulled quite a few motors down where it was 1 tooth out.
1 tooth = 18° at crank... it's a lot!
Author:  Wombat [ Sun Jan 31, 2010 9:19 am ]
Post subject: 
When I first saw the pic I thought the marks were not quite lined up but dismissed it as my lack of knowledge in that area - then saw Matt and David's responses and now know why they make off set keys :roll:
Author:  david rosenthal [ Tue Feb 02, 2010 12:24 am ]
Post subject: 
I made a 1" bar with a keyway cut along it and collected up all the crank sprockets I had and stacked them on top of each other to check the relationship between the position of the keyway and the tip of the tooth.
It is interesting that there was quite a degree of discrepancy between sprockets. some were half a tooth different. There also seemed to be slight differences between earlier/later engines and also between 850/998/and 1100. Probably would not matter for a std engine having the cam timing out a few degrees but when you are chasing performance every little bits helps.
As wombat said stepped keys or vernier adjustment solves this problem.
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